The parenteral administration of sterile fluids is an established clinical practice, and the practice is used extensively as an integral part of the daily treatment of medical and surgical patients. The fluids administered parenterally, usually intravenously, include aqueous solutions of dextrose, sodium chloride, and various other electrolytes. Always administered intravenously are blood and blood substitutes. Generally, the fluids are administered from a container that is suspended above a patient, with the fluid flowing from the container through an administration set and thence to a cannula or a hypodermic needle placed in a blood vessel, usually a vein of the patient. For intraperitoneal administration of fluids, the administration set is connected to a cannula traversing the abdominal wall of the patient.
The administration of fluids parenterally is a valuable and important component of patient care. The use of parenteral fluids moreover has in recent years expanded beyond its original role of fluid and electrolyte replacement to include serving as the vehicle for the parenteral administration of beneficial agents, notably for those where it is desirable to administer by infusion via the intravenous, intra-arterial, intrapertioneal or subcutaneous routes. For example, presently a beneficial agent, such as a drug, is administered intravenously by one of the following procedures: temporarily halting the flow of medical fluid and intravenously administering a solution of the drug to the patient through an injection port in the administration set, followed by resumption of medical fluid into the patient; a drug is added to the fluid in the container, or into a volume control chamber in series with the administration set, and then carried by the flow of fluid into the patient; a drug is introduced into a so-called "piggyback" container, which is subsequently connected via a connector, in tributary fashion, to the primary. administration set through which fluid is administered to the patient; or a drug is administered by a pump which, by one of various recognized pumping actions, establishes flow and this determines the flow of fluid containing the drug into a flow path entering the patient, for example, an indwelling venous catheter.
While these techniques are widely used, they have certain inherent disadvantages. For example, the administration of a drug through repeated injections into the administration set is inconvenient and represents each time a potential break in sterility; the use of pumps is expensive and sometimes inconvenient because of their size and weight; the rate of drug delivery to the patient is dependent on the flow of fluid with all currently practiced means of drug infusion; because of the relative chemical instability of aqueous solutions of many parenteral drugs, these procedures often require solubilization of the drug medication by the hospital pharmacist or by the nurse at a time proximate to its administration; and, while it is current practice to give some drugs by brief infusions, typically of 30 to 120 minutes duration repeated 3 or 4 times a day, they do not provide a means for (a) careful coordination of the procedures for solubilization and administration, (b) careful regulation of the flow of drug solution during each period of infusion to insure that infusion is completed within the recommended time, and (c) for doses prepared in advance and administered at a preselected time.
In view of this presentation, it is immediately apparent a critical need exists for a dependable and practicable parenteral therapeutic delivery system that overcomes the disadvantages associated with the systems known to the prior art. It is also apparent that a pressing need exists for a parenteral delivery system that can be used clinically for administering parenterally a beneficial agent at a controlled rate and in a beneficially effective amount to a patient according to a preselected program comprising continuous administration, repeated administration, administration at specified intervals, or as needed administration.